Simplify deep_ast_copy.
Simplify deep_ast_copy.

mfussenegger/jedi,WoLpH/jedi,dwillmer/jedi,jonashaag/jedi,dwillmer/jedi,WoLpH/jedi,flurischt/jedi,jonashaag/jedi,flurischt/jedi,mfussenegger/jedi,tjwei/jedi,tjwei/jedi